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ftbratia  Uutautlp, 

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WHAT  CAUSES  FATIGUE? 

AN  ADDRESS 
BY  THOMAS  DARLINGTON,  M.D. 


WHAT  CAUSES  FATIGUE? 


AN  ADDRESS 

BY 

THOMAS  DARLINGTON,  M.D. 

NEW    YORK 

SECBETARY,    WELFARE    COMMITTEE,    AMERICAN    IRON    AND    STEEL    INSTITUTE;     FORMERLY 

COMMISSIONER    OF    HEALTH    OF    NEW    YORK    CITY;     MEMBER    OF    THE    AMERICAN 

MEDICAL    ASSOCIATION,    THE  NEW  YORK  ACADEMY  OF  MEDICINE,  ETC. 


MEETING  DELIVERED   AT 

THEMHVMHOF  THE  AMERICAN  IRON  AND  STEEL  INSTITUTE 

WALDORF-ASTORIA   HOTEL,    NEW  YORK 
MAY   23,   1913 


THE   TROW    PRESS 
NEW    YORK 


WHAT  CAUSES  FATIGUE? 
Thomas  Darlington,  M.D. 

Secretary,  Welfare  Committee.  American  Iron  and  Steel  Institute. 

In  modern  industry  there  is  no  question  of  more  impor- 
tance, so  far  as  human  activity  is  concerned,  than  that  of 
bodily  fatigue.  A  review  of  the  causes  of  fatigue  and  of 
remedial  measures  looking  to  prevention  of  over-tiredness  is 
therefore  appropriate  at  this  meeting. 

It  needs  no  scientist  to  tell  us  that  the  proper  use  of 
muscle  increases  its  power  for  work,  that  proper  exercise 
increases  strength.     As  Josephine  Goldmark  has  well  said: 

Work  itself  is  of  the  essence  of  life;  without  it,  man's 
physical  as  well  as  his  moral  nature  decays.  Regular  con- 
tinuous labor  and  exertion  is  as  necessary  for  the  worker's 
health  as  it  is  for  subsistence. 

Some  Physiological  Facts. 

To  understand  fatigue,  and  the  various  factors  of  its 
causation,  we  must  understand  certain  physiological  facts. 
In  the  living  body  there  is  constant  change.  Constantly 
there  is  a  building  up  process;  constantly  there  is  a  breaking 
down  and  wasting  process.  Even  though  there  be  but  little 
bodily  movement  or  exertion,  still  the  glands  are  secreting, 
still  there  is  production  of  heat.  The  chemical  changes  that 
take  place  are  known  as  metabolism,  the  building  up  process 
being  called  anabolism,  and  the  breaking  down  process 
catabolism.  - 

In  the  muscles  particularly  such  chemical  changes  are 
constantly  taking  place.  These  changes  take  place  more 
rapidly  when  the  muscles  are  in  action,  that  is,  when  the 
muscles  contract.  Every  exertion  and  muscular  contraction 
causes  the  expenditure  of  energy.  Every  muscle  contains  in 
itself  latent  energy  in  fuel  to  be  converted  into  mechanical 
energy  and  heat.  This  fuel  is  supplied  from  the  blood  and  is 
in  the  form  of  sugar  (dextrose  CJluOe),  animal  starch  (gly- 
cogen C6H10O&),  and  fat. 

1 


The  living  substance  of  muscle  has  the  power  of  burning 
up  sugar.  In  this  process  lactic  acid  and  ultimately  carbon 
dioxide  and  water  are  formed.  Thus,  dextrose  changes  to 
lactic  acid — C6Hi206  (dextrose)  =2  (C3Ha03)  (lactic  acid)  — 
and  the  lactic  acid  is  finally  broken  down  into  carbon  dioxide 
and  water. 

Muscle  is  made  to  contract  by  stimulation.  This  stimu- 
lation is  through  impulse,  from  the  brain  or  other  parts  of 
the  nervous  system.  It  may  primarily  arise  from  the  will, 
and  secondarily  from  heat,  from  cold,  from  electricity  or 
from  other  causes.  When  a  muscle  contracts  more  oxygen 
is  used  and  more  carbon  dioxide  is  discharged  than  when  it  is 
resting.  A  normal  resting  muscle  is  alkaline  in  its  reaction, 
but  after  a  number  of  rapid  contractions  it  becomes  acid  in 
its  reaction. 

The  materials  for  building  up  the  tissues  are  carried  to 
the  various  portions  of  the  body  by  the  blood  stream,  and 
the  products  of  waste  are  carried  away  from  the  tissues  by 
the  same  means. 

The  oxygen  necessary  for  combustion — that  is,  for  chemi- 
cal transformation  in  the  production  of  energy — is  carried 
by  the  red  material  in  the  blood  (haemoglobin)  to  the  tissues. 
The  red  material  there  gives  off  some  of  its  oxygen,  and  the 
blood  takes  up  carbon  dioxide,  which  it  carries  back  to  the 
lungs  to  be  eliminated. 

The  liver  normally  forms  sugar  and  glycogen,  or  animal 
starch,  a  substance  readily  converted  into  sugar.  Muscle 
tissue  is  capable  of  storing  up  in  the  form  of  glycogen  much 
of  the  sugar  brought  to  it.  Glycogen  is,  therefore,  a  normal 
constituent  of  the  muscles. 

In  some  respects  the  development  of  energy  in  the  body 
is  analogous  to  the  development  of  steam  in  a  boiler  or  the 
operation  of  a  gas  engine.  There  must  be  fuel,  such  as  coal, 
oil  or  gas;  there  must  be  a  supply  of  air  containing  oxygen; 
and  there  are  the  ashes  as  waste. 

From  the  above  it  is  obvious  that  muscular  energy  de- 
pends largely  upon  three  things: 

1.  The  amount  of  fuel  stored  and  the  ability  of  the  system 
to  bring  it  into  use. 

2 


2.  The  ability  of  the  system  to  furnish  oxygen  to  burn 
the  fuel. 

3.  The  ability  of  the  system  to  carry  off  waste  or  other 
toxic  substances. 

Conversely,  fatigue  is  due  primarily  to  the  failure  of  the 
system  to  perform  properly  one  or  more  of  these  functions. 

Storage  of  Fuel. 

First,  fatigue  may  be  caused  by  anything  that  interferes 
with  the  storage  of  fuel.  This  may  arise  from  a  lack  of  fuel. 
Under  this  head  would  come  underfeeding,  improper  feeding* 
indigestion  of  food,  lack  of  assimilation  ol  food,  and  in- 
capacity of  the  liver  and  muscles  to  store  sufficient  glycogen. 

It  requires  no  argument  to  prove  that  if  fuel  is  lacking 
energy  must  also  be  lacking.  So  if  one  does  not  have  suffi- 
cient food,  he  cannot  store  enough  energy.  This  may  also 
be  the  case  when  a  large  enough  quantity  is  eaten  but  not 
of  the  proper  kind  or  quality.  One  has  learned  much  who 
has  learned  what  food  to  purchase.  For  example,  cabbage 
is  a  very  common  article  of  diet  but  there  is  little  energy 
to  be  derived  from  it.  We  should  all  study  food  values  and 
how  and  what  to  purchase  in  order  to  get  the  most  and  the 
best  for  our  money. 

It  is  impossible  in  this  paper  to  go  into  all  the  details  of 
the  digestibility  of  different  foods. 

To  regulate  the  food  according  to  the  demands  of  the 
body,  to  have  a  properly  balanced  dietary,  comes  only  as 
the  result  of  study.  Education  along  these  lines  in  connec- 
tion with  industrial  plants  is  best  given  in  the  form  of  house- 
hold instruction  by  trained  nurses  or  domestic  educators. 

True,  since  Knoop  has  shown  that  the  system  can  change 
one  food  into  another,  an  excess  of  one  kind  of  food  is 
probably  converted  in  the  system  into  others.  But  physio- 
logical tests  have  shown  that  a  mixed  diet  is  best  for  the 
needs  of  the  system.  The  body  is  very  adaptable  but  we 
should  not  put  upon  it  unnecessary  alimentary  burdens. 

Pavlov  has  shown  that  the  secretion  of  the  gastric  juice 
depends  largely  on  the  character  of  food  and  on  appetite. 

All  of  these  things  relate  to  the  question  of  the  wise 

3 


selection  of  food  for  energy  and  the  needs  of  the  system. 
An  examination  of  many  lunch  buckets  has  indicated  to  me 
that  sometimes  but  little  thought  is  given  as  to  the  kind  of 
food  that  goes  into  them,  provided  there  is  quantity.  Many 
times  the  food  in  lunch  buckets,  such  as  yeast  bread,  becomes 
sweated,  and  milk  in  the  coffee  undergoes  more  or  less  fer- 
mentation.    This  bears  directly  upon  energy. 

After  food  reaches  the  stomach  there  is  often  much  need- 
less waste,  particularly  of  the  sugars,  due  to  fermentation  in 
the  stomach.  The  sugars  are  split  into  acids  before  reaching 
the  tissues  and  so  are  partly  lost  for  energy.  The  fermenta- 
tion is  due  to  two  causes:  First,  to  a  lack  of  gastric  juice;  and 
second,  to  an  excess  of  bacteria.  A  lack  of  gastric  juice,  and 
therefore  indigestion,  is  due  to  an  improper  selection  of  food, 
to  a  disturbed  mental  condition  (anger,  grief,  worry)  or  to 
reflex  disturbances  of  the  gastric  nerves,  from  chronic  appen- 
dicitis, etc.  Or  there  may  be  an  excess  of  bacteria.  This 
is  due  either  to  fermented  or  putrid  foods,  or  to  the  addition 
of  bacteria  to  the  food  from  unclean  mouths  and  bad  teeth 
or  dirty  hands.  Over-eating  and  rapidity  of  eating  also 
affect  digestion  and  therefore  promote  fatigue. 

Assimilation  of  food  varies  in  different  persons.  The 
capacity  of  the  liver  or  of  the  muscles  to  store  glycogen  must 
depend  somewhat  on  their  size  and  the  size  of  a  muscle 
depends  largely  upon  its  use. 

To  combat  fatigue  from  these  causes  it  would  be  well  to 
have  at  plants  dining  rooms  and  restaurants,  with  freshly 
and  properly  prepared  and  well  selected  foods,  furnished  at 
the  lowest  practicable  price,  served  under  cheerful  and 
pleasant  surroundings,  and  with  sufficient  time  to  eat. 

A  Lack  of  Oxygen  Causes  Fatigue. 

Secondly,  fatigue  is  caused  by  anything  that  interferes 
with  the  carrying  of  oxygen  to  the  tissues.  This  may  be 
a  diminished  amount  of  oxygen  in  the  atmosphere,  dimin- 
ished carrying  power  of  the  blood,  diminished  lung  capacity, 
or  interference  with  the  circulation  of  the  blood. 

The  two  factors  which  relate  especially  to  diminished 
amount  of  oxygen  in  the  atmosphere  are  bad  ventilation 

4 


and  altitude.  The  main  effect  of  bad  ventilation,  especially 
where  there  are  a  number  of  people  in  a  room,  is  to  increase 
the  humidity.  The  detrimental  effect  of  this  humidity, 
which  will  be  considered  at  greater  length  later  in  this  paper  3 
is  of  more  importance  than  any  diminishing  of  oxygen  or  in- 
crease in  carbon  dioxide. 

From  diminished  oxygen,  altitude  produces  fatigue. 
Anyone  who  has  climbed  a  mountain  has  felt  this. 

In  industry  we  are  more  concerned,  however,  with  the 
diminished  oxygen  carrying  power  of  the  blood.  As  before 
stated,  oxygen  is  carried  to  the  tissues  by  the  blood,  which 
also  carries  carbon  dioxide  from  the  tissues  to  the  lungs  to 
be  eliminated. 

There  is  a  great  difference  in  people  as  to  the  number 
of  red  corpuscles  in  the  blood,  and  therefore  in  its  oxygen- 
carrying  power.  Some  people  have  only  half  as  many  red 
corpuscles  as  others.  If  these  red  corpuscles  are  much  di- 
minished the  condition  is  called  anaemia.  Leaving  out  the 
question  of  loss  of  blood,  anaemia  is  produced  by  a  variety 
of  causes,  among  which  are  deficient  light,  insufficient  iron 
in  the  blood,  insufficient  variety  of  food,  irregularity  of  the 
bowels,  as  the  sequel  of  disease  (particularly  infectious  dis- 
ease) and  of  metal  poison,  such  as  lead.  So,  working  at  night, 
or  in  dark  buildings  or  dark  rooms,  is  injurious  to  the  blood. 

Carbon  Monoxide. 

A  matter  of  particular  importance  to  those  in  the  iron  and 
steel  industry  is  the  fact  that  the  oxygen-carrying  power  of 
the  blood  is  very  much  diminished  if  there  is  any  carbon 
monoxide  in  the  air  breathed  by  the  men.  The  deleterious 
effect  of  this  gas  is  due  to  its  combination  with  the  red  ma- 
terial in  the  blood,  thus  injuring  the  oxygen-carrying  function. 
The  affinity  of  the  red  material  of  the  blood  for  carbon 
monoxide  is  much  greater  than  its  affinity  for  oxygen,  form- 
ing a  compound  with  carbon  which  is  a  much  more  stable 
compound  than  that  formed  with  oxygen. 

Carbon  monoxide  often  produces  a  fatal  effect.  So  we 
must  guard  against  poisoning  by  this  gas.  This  is  a  product 
of  the  furnaces  and  is  especially  dangerous  in  bad  weather, 

•       5 


coming  down  the  side  of  the  furnaces.  It  also  occurs  in 
engine  rooms  from  leaky  gas  engines ;  and  we  find  it  in  plants 
where  open  fires,  such  as  salamanders,  are  used  for  heating 
purposes  in  winter,  or  from  blacksmiths'  fires.  Even  though 
the  quantities  breathed  are  small  this  gas,  breathed  con- 
stantly, will  in  time  produce  anaemia.  So  gas  engines  should 
be  watched.  For  heating  purposes  other  methods  than  open 
fires  should  be  adopted.  And  blacksmiths'  fires  should  be 
hooded  to  carry  away  gases. 

Anything  that  interferes  with  the  general  circulation  of 
the  blood,  such  as  heart  disease,  tight  clothing  or  the  con- 
dition of  the  body,  causes  fatigue.  Where  there  is  diminished 
lung  capacity,  as  in  consumption  of  the  lungs  (phthisis), 
there  is  interference  with  the  oxygen  carrying  power  of  the 
blood.  In  heart  disease  the  blood  is  not  properly  pumped 
through  the  body.  In  the  case  of  obese  persons  the  in- 
crease of  the  vessels  and  the  distance  for  the  blood  to  travel 
make  the  heart  pump  harder.  Tight  clothing  directly  in- 
terferes with  the  circulation.  All  these  cause  fatigue.  Age, 
sex,  climate  and  seasons  also  have  much  to  do  with  the 
circulation  of  the  blood,  and  therefore  with  fatigue. 

Accumulation  of  Waste  Causes  Fatigue. 

The  third  great  cause  of  fatigue  is  poisoning  by  ac- 
cumulated waste  in  the  muscles  or  poisoning  by  toxic  sub- 
stances. This  accumulation  may  be  due  to  too  rapid  forma- 
tion of  the  products  of  waste,  or  it  may  be  due  to  the  inability 
of  the  blood  or  system  to  carry  away  the  waste  products. 
If  the  nerve  of  a  muscle  is  constantly  stimulated,  the  mus- 
cular contractions  become  smaller  in  extent  and  finally 
cease.  The  muscle  is  then  said  to  be  fatigued.  The  sugars 
and  glycogen  have  been  burned,  producing  energy  and  leav- 
ing as  wastes  carbon  dioxide  and  lactic  acid.  Unless 
eliminated  these  materials  act  as  poisons. 

When  a  muscle  is  fatigued  there  is  more,  however,  to 
be  considered  than  the  local  poison.  The  products  of 
fatigue  pass  into  the  blood  and  poison  all  parts  of  the  body, 
including  the  nervous  system.  The  question  has  been 
carefully  studied  by  a  number  of  able  and  well-known  in- 

6       • 


Fig.  1.- 


-Mosso's  ergograph  for  measuring  fatigue. 

(Courtesy  of  G.  P.  Putnam's  Sons.) 


vestigators.  Special  mention  should  be  made,  in  the  chrono- 
logical order  of  their  investigations,  of  those  by  Ranke  and 
Helmholtz  and  Mosso  and  those  by  Professor  Lee  of  Colum- 
bia University,  whose  more  recent  investigations  have  shed 
much  light  upon  the  intricate  problems  connected  with 
this  subject. 

It  has  been  shown  by  Mosso,  late  professor  of  physiology 
in  the  University  of  Turin,  that  the  introduction  of  the 
blood  of  a  fatigued  animal  into  the  circulation  of  one  not 
fatigued  will  give  rise  to  all  the  symptoms  of  fatigue  in  the 
normal  animal.  Mosso  devised  an  instrument  called  the  ergo- 


Fig.  2. — The  registering  runner  of  the  ergograph. 

(.Courtesy  of  G.  P.  Putnam's  Sons.) 

7 


graph.  (See  Figures  1  and  2.)  In  this  instrument  the  arm, 
the  hand  and  all  the  fingers  but  one  are  held,  and  the  free 
finger  rapidly  lifts  a  weight  over  a  pulley.  A  marker  moving 
over  a  smoked  surface  registers  the  height  to  which  it  is 
raised.  Experiments  carried  on  in  these  ways  show  that  the 
state  of  the  brain,  the  central  nervous  system,  as  well  as  the 


=©=i 


Fig.  3. — Apparatus  for  registering  contractions  of  electrically  stimulated 

muscle.     (Courtesy  of  Professor  F.  S.  Lee.) 

condition  of  the  muscles,  are  important  factors  in  fatigue. 
The  poisons  produced  diminish  the  power  to  send  out 
nervous  impulses. 

Experiments  on  muscles  removed  from  animals  and 
stimulated  by  an  electric  current  are  also  made  and  the  re- 
sults are  recorded.     (See  Figure  3.) 

Drinking  of  Water  Lessens  Fatigue. 

Perhaps  no  means  of  lessening  fatigue  is  of  more  im- 
portance than  a  proper  supply  of  drinking  water.     The 

8 


products  of  waste,  carbon  dioxide  and  lactic  acid,  are  taken 
up  by  the  fluids  of  the  body  and  carried  to  the  lungs 
and  kidneys  for  elimination.  The  accumulation  of  waste 
products  is  often  due  to  insufficient  use  of  drinking  water. 
It  has  been  noticed  in  the  army  that  the  man  who  falls  from 
heat  stroke  is  the  one  whose  canteen  is  empty. 

Poisons  that  are  very  dilute  have  as  a  rule  but  little  detri- 
mental effect  upon  the  system.  The  most  powerful  acids  if 
sufficiently  diluted  with  water  are  no  longer  caustic.  And 
self-generated  poison  in  the  body  will,  if  sufficiently  diluted, 
probably  have  less  effect. 

Some  years  ago  in  my  service  at  Fordham  Hospital,  a 
number  of  cases  of  typhoid  fever  under  my  direction  were 
given  an  average  of  120  cubic  centigrams  of  a  normal 
salt  solution  in  a  vein.  The  effect  almost  invariably  was 
to  reduce  the  temperature  of  the  patient  to  normal;  and 
patients  so  treated  progressed,  as  a  rule,  favorably  toward 
recovery. 

It  would  seem  reasonable  to  suppose  that  the  beneficial 
effects  of  the  saline  solution  were  produced  in  two  ways: 
first,  by  dilution  of  the  poison;  second,  by  increased  elimi- 
nation by  the  skin  and  kidneys.  The  danger  of  destroying 
living  cells  and  tissues  by  high  temperature  and  by  the  toxin 
of  typhoid  was  thus  largely  eliminated.  This  is  one  illustra- 
tion of  the  importance  of  having  in  connection  with  every 
plant  a  proper  water  supply. 

Some  caution,  however,  is  necessary.  Water  is  not 
readily  absorbed  in  the  stomach  but  passes  quickly  into 
the  intestines.  If  water  is  too  cold,  it  is  retained  for  a 
longer  time  in  the  stomach  and  its  benefits  are  not  so 
quickly  felt.  Sometimes  if  water  is  too  cold  it  brings  on 
cramps,  and  sometimes  if  too  large  a  quantity  is  taken  it 
is  rejected.  So  the  water  supply  for  drinking  purposes 
must  not  only  be  pure  in  quality  and  ample  in  quantity, 
but  it  must  be  kept  at  the  proper  temperature. 

Cold  Showers  Lessen  Fatigue. 

Not  only  internally  but  also  externally  water  plays  a 
part  in  lessening  fatigue.     So  the  benefits  derived  from 

9 


general  bathing  should  be  mentioned.  These  have  been 
recognized  for  many  centuries,  and  the  therapeutic  use  of 
the  bath  is  as  old  as  the  art  of  medicine  itself.  The  public 
baths  of  the  Greeks  and  Romans  were  a  prominent  feature 
of  their  civilization.  Recently  hydrotherapy  has  received 
much   study   and   has   become   more   of   a   science.     The 


Fig.  4.  Fig.  5.  Fig.  6. 

Fig.  4. — Normal  fatigue  curve.     (After  Vinaj.) 

Fig.  5. — Fatigue  curve  of  same  after  work. 

Fig.  6. — Same  after  cold  douche,  showing  restoration  to  normal. 

capacity  of  water  for  heat  makes  it  valuable  for  use  in  ex- 
tracting heat  or  in  applying  heat. 

As  the  skin  covers  a  network  of  blood  vessels  and  nerves, 
water  can  be  used  to  affect  a  physical  reaction. 

In  general,  the  application  of  cold  causes  the  blood 
vessels  to  contract  and  heat  causes  them  to  dilate.  Such 
stimulation  of  the  skin  affects  not  only  the  surface  of  the 
body  but  also  the  nerves  and  blood  vessels  of  the  whole 
system.  And  stimulation  of  certain  areas  of  the  skin  affects 
directly  certain  internal  organs.     Such  stimulation  of  the 

10 


skin  influences  both  the  voluntary  and  the  involuntary- 
muscles.  Experiments  upon  the  human  body,  recorded 
by  the  ergograph,  have  proven  that  in  general  cold  applica- 
tions increase  resistance  to  fatigue  and  that  they  restore  effi- 
ciency for  work  to  a  muscle  already  fatigued.  (See  Figures 
4-8.)  This  increase  in  muscle  tone  produces  a  redistribution 
of  the  blood  in  the  body.  Conversely  experiments  show  that 
a  warm  bath  lessens  efficiency.     (See  Figures  9  and  10.) 

By  means  of  shower  baths  the  skin  is  mechanically  stim- 
ulated by  the  striking  drops.  This  combined  with  thermic 
influence  increases  the  effect  of  the  bath  upon  the  heart  and 
respiration.  It  also  affects  metabolism.  It  increases  the 
production  of  animal  heat.  The  heart  action  is  increased 
in  force.  The  secretion  of  the  skin  is  diminished.  It  in- 
creases the  urine  and  other  internal  secretions.  Examina- 
tion of  the  blood  shows  certain  changes  in  the  elements  of 


Fig.  7.  Fig.  8. 


Fig.  7. — Normal  fatigue  curve  of  the  hand.     (After  Maggiora  and  Vinaj.) 
Fig.  8. — Normal  fatigue  curve  of  the  hand  after  a  slowly  cooled  bath. 


the  blood  itself.     Thus  water,   through  the  skin,   affects 
secretion,  excretion  and  the  heat  regulating  function. 

Shower  baths  may,  therefore,  be  used  to  eliminate  more 
rapidly  the  products  of  waste,  to  promote  secretion,  to  re- 
lieve fatigue,  to  restore  the  normal  functions  to  various 
organs  of  the  body,  to  restore  the  body  temperature  to  the 
normal,  and  to  produce  a  redistribution  of  the  blood  when 
there  is  congestion  in  any  one  part  of  the  body. 

11 


Fig.  9. — Normal  fatigue  curve. 

(Courtesy  of  Dr.  J.  If.  Kellogg ■) 

Heat  and  Humidity  Affect  Body  Temperature. 

Everyone  knows  that  on  a  hot,  humid  day,  a  man  is 
much  less  efficient  than  on  a  cool,  dry  day.  The  reason  for 
this,  however,  has  only  recently  been  shown  by  scientific 
investigation.  Ordinarily  body  temperature  is  maintained 
at  a  fixed  level  with  but  little  deviation.  The  control  of  the 
production  of  heat  and  the  regulation  of  its  dissipation  rest 
primarily  in  the  brain  and  nervous  system.  On  hot  days 
when  there  is  excessive  humidity,  the  body  temperature  rises. 
Rise  of  temperature  may  occur  in  three  ways:  Heat  produc- 


Fig.  10. — Fatigue  curve,  same  subject,  after  a  hot  bath. 

(Courtesy  of  Dr.  J.  H.  Kellogg.) 

12 


tion  may  increase  while  heat  loss  remains  constant,  or  heat 
production  may  remain  constant  while  heat  loss  may  be  di- 
minished, or  heat  production  may  increase  while  heat  loss 
diminishes.  There  is  increase  of  heat  production  after  the 
absorption  of  a  full  meal.  Muscular  work  also  increases 
heat  production  enormously. 

In  general,  heat  production  results  from  the  combination 
of  oxygen  with  carbon  and  hydrogen,  forming  carbon  dioxide 
and  water.  In  other  words,  oxidation  is  the  source  of  heat 
production. 

On  exposure  to  external  heat  the  blood  vessels  of  the  skin 
become  dilated  and  the  sweat  glands  become  active. 

By  radiation,  by  conduction,  and  by  the  evaporation  of 
water,  there  is  loss  of  body  heat  from  the  skin.  Heat  is  also 
lost  by  the  moisture  of  the  breath.  When  there  is  much 
humidity,  sufficient  to  prevent  evaporation  of  sweat  and 
the  elimination  of  the  heat  which  is  constantly  being  pro- 
duced within  the  body,  the  internal  temperature  rises  and 
fever  results.  The  elimination  of  heat  by  the  breath  also 
depends  somewhat  on  humidity.  Dr.  Denison,  of  Denver, 
has  shown  that  fully  eight  ounces  more  water  is  lost  by  the 
breath  during  twenty-four  hours  in  Denver  than  in  New 
York.  And  according  to  my  own  experience  and  observa- 
tion in  Arizona,  this  amount  is  increased  in  that  drier  climate. 
Conversely,  on  a  humid  day  we  do  not  eliminate  as  much 
moisture  by  the  lungs.  Heavy  clothes  preventing  evapora- 
tion from  the  skin  increase  this  rise  of  temperature. 

Observation  of  those  who  work  in  heat  and  excessive 
humidity  shows  that  they  soon  pass  into  a  condition  of 
fatigue.  That  is,  fever  produces  a  condition  of  fatigue- 
This  fatigue  which  comes  from  fever  is  brought  about  by  the 
energy-forming  materials  in  the  muscles  being  burned  up 
rapidly  and  the  poisonous  products  of  such  combustion 
accumulating  within  the  body.  And,  what  is  of  great  im- 
portance, if  there  is  not  a  sufficient  amount  of  carbohydrates 
for  use  there  is  destruction  of  protein  material  similar  to 
that  found  in  excessive  work,  due  to  the  direct  action  of  high 
temperature.  In  addition,  the  blood  is  drawn  to  the  sur- 
face of  the  body,  leaving  the  brain,  the  spinal  cord,  and  the 

13 


internal  organs  correspondingly  ansemic.  This  lessens  the 
normal  impulses  to  the  muscles,  and  in  itself  will  give  a  tired 
feeling. 

Other  poisons  besides  those  generated  in  the  muscles 
produce  fatigue.  Fermentations  in  the  intestinal  canal  pro- 
duce poisons  which  have  a  fatiguing  effect.  Thus  indol,  and 
possibly  other  substances,  have  been  proven  to  induce 
(See  Figure  11.)  Indol  is  BHHBHHl 
found  in  the  large  intestine  as  the  result  of  bacterial  putre- 
faction. It  is  eliminated  in  part  from  the  bowels;  but  is  in 
part  absorbed  in  the  blood  and  subsequently  eliminat 


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Fig.  11. — The  upper  record  shows  the  normal  fatigue  curve  of  a  muscle.  The 
lower  record  shows  the  fatiguing  effect  of  indol.  (This  illustration  has 
never  before  been  published  and  is  shown  here  by  the  courtesy  of  Pro- 
fessor F.  S.  Lee.) 

the  urine,  in  the  form  of  indican.  As  indol  is  produced 
by  the  fermentation  of  certain  kinds  of  albuminous  foods, 
diet  is  again  an  important  factor.  That  the  products  of 
waste  in  the  intestinal  canal  should  be  rapidly  excreted  is 
self-evident. 

Other  abnormal  substances  are  sometimes  formed  in  the 
digestive  tract,  such  as  B.  oxybutyric  acid  and  diacetic  acid 
and  oxalic  acid,  made  from  fats  and  carbohydrates.  These 
undoubtedly  also  bear  upon  the  question  of  fatigue. 

Effect  of  Lack  of  Sleep. 

Sleep  is  the  period  of  repair  and  growth,  the  time  when 
the  building  up  process  exceeds  the  breaking  down  process. 
During  sleep  less  carbon  dioxide  is  eliminated  and  less  oxygen 

14 


is  absorbed.  Experiments  upon  dogs  show  that  if  starved  even 
for  several  weeks  they  will  recover,  but  that  they  die  from  loss 
of  sleep  in  five  days.  Loss  of  sleep  is  much  more  damaging 
than  starvation.  Loss  of  sleep  is  a 
common  cause  of  fatigue. 

Thus  badly  ventilated  rooms, 
and  over-heated  rooms  in  summer, 
crowding  of  rooms,  with  noise  and 
other  discomforts,  and  the  hours 
of  sleep  are  matters  requiring  care- 
ful consideration  by  those  who 
employ  labor. 

Fatigue  Lessens  Resistance 
to  Disease. 

One  of  the  most  important  re- 
sults of  fatigue  is  that  it  lessens 
resistance  to  disease.  It  has  been 
shown  that  after  the  death  of  an 
animal  from  fatigue  the  body  under- 
goes rapid  putrefaction.  Clinical 
experience  and  experiments  on  ani- 
mals (see  Figure  12)  have  shown 
that  people  who  are  fatigued  are 
much  more  subject  to  contagious 
and  infectious  diseases. 

There  is,  therefore,  a  physiological,  a  chemical  and  a 
psychological  basis  of  fatigue. 

Conclusion. 

If  a  muscle  is  fatigued  from  too  rapid  movement  or  from 
too  long  continued  use,  or  if  it  is  pushed  in  use  when  it  is 
already  fatigued,  changes  take  place  which  affect  the  protein 
of  the  muscle  and  it  is  long  in  recuperating.  After  a  double 
task,  muscle  requires  four  times  as  long  as  normal  to  re- 
cover. Work  that  is  too  hard  and  too  long  continued  is 
harmful.  Ambitious  workmen  doing  piece  work  will  some- 
times produce  this  result  by  speeding  beyond  the  limits 
which  nature  prescribes.     (See  Figure  13.) 

15 


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fatigue.      (Courtesy  of  Professor 
F.  S.  Lee.) 


But  we  must  not  charge  to  work  what  is  properly  charge- 
able to  other  causes.  Ordinary  tiredness  resulting  from 
proper  effort  is  not  harmful  but  beneficial,  enabling  us  to 
enjoy  and  digest  our  food  and  obtain  rest  and  recuperation 
from  sleep.  Work  in  itself  is  a  joy  and  a  blessing.  It  pro- 
motes longevity.  As  a  rule  people  who  work  hard  are  not 
troubled  with  either  indigestion  or  insomnia.  Sound  and 
true  is  the  saying  of  Ecclesiastes,  "The  sleep  of  a  labouring 
man  is  sweet,  whether  he  eat  little  or  much;  but  the  abun- 
dance of  the  rich  will  not  suffer  him  to  sleep." 


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Fig.  13. — Curves  showing   that   rapidity   of   work  beyond   a  certain  point 

quickly   produces   fatigue.     (Courtesy  of  Professor  F.  S.  Lee.) 

Showerbaths  and  other  methods  of  relieving  fatigue 
should  not  be  installed  to  spur  men  on  to  work  when  they 
ought  to  rest.  Showerbaths  are  especially  for  use  at  the  end 
of  the  day,  to  promote  recuperation.  They  are,  as  a  rule, 
not  to  be  used  during  the  day  except  under  medical  advice 
and  direction. 

The  aim  of  employer  and  employee  alike  should  be  to  do 
away  with  improper  causes  of  fatigue,  to  the  end  that  the 
workman  may,  in  the  interest  of  all  concerned,  do  the  best  of 
which  he  is  capable,  thus  growing  in  strength  and  in  the 
power  to  achieve. 

The  conclusion  is  that  both  fatigue  and  efficiency  depend 
upon  the  fundamentals  of  hygiene  more  than  upon  exercise 
alone,  and  that  our  aim  should  be,  to  use  the  words  of 

16 


Professor  Lee,  "  to  make  of  labor  a  physiological  rather  than  a 
pathological  exercise."  Thus  shall  we  be  able  to  obey  the 
injunction  of  the  apostle  Paul:  "Quit  you  like  men;  be 
strong."     In  the  language  of  Maltbie  Babcock, 

We  are  not  here  to  play,  to  dream,  to  drift; 
We  have  hard  work  to  do  and  loads  to  lift. 
Shun  not  the  struggle;  face  it.     Tis  God's  gift. 


17 


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